1. Field of the Invention
This invention relates generally to a direct current power supply device, and, more particularly to a direct current power supply device for rectifying the output voltage of an external a-c power supply such as an engine generator to supply power to a d-c load and/or a battery, wherein control is exerted to give a predetermined current-voltage characteristic, and a leakage transformer is used.
2. Description of the Prior Art
A recreational vehicle such as a mobile home usually has a d-c power supply device which supplies power from a battery to a d-c load during running, and supplies power to the d-c load/and/or the battery via a converter when an external a-c power supply or an engine generator is available.
In charging the battery, the d-c power supply device is generally designed to provide a constant current-constant voltage characteristic to the converter. The d-c power supply device of this type is subject to relatively large voltage fluctuations due to the source voltage fluctuations in an engine generator which is used as an a-c power supply. Even when an external a-c power supply is used, voltage fluctuations become extremely large if an a-c load such as an air conditioner having a relatively large capacity is turned on and off from time to time. In addition, the temperature in this type of d-c power supply device tends to rise due to the above-mentioned voltage increase.
Taking into consideration the above-mentioned voltage fluctuations and temperature rise, the conventional d-c power supply device usually uses circuit elements having a relatively large capacity, which causes cost to rise and the size of the device to increase.
Furthermore, in the conventional d-c power supply device, it is difficult to obtain desired constant current-constant voltage characteristic due to the above-mentioned voltage fluctuations and/or temperature rise.
In addition, when a battery with an extremely low terminal voltage is charged in this type of d-c power supply device, an excess current is produced, damaging the battery and circuit elements, particularly semiconductor elements. For this reason, it is desired to protect circuit elements against excess current.